\Header{help.search}{Search the Help System}
\alias{print.hsearch}{help.search}
\keyword{documentation}{help.search}
\begin{Description}\relax
Allows for searching the help system for documentation matching a
given character string in the (file) name, alias, title, or keyword
entries (or any combination thereof), using either fuzzy matching or
regular expression matching.  Names and titles of the matched help
entries are nicely displayed.\end{Description}
\begin{Usage}
\begin{verbatim}
help.search(pattern, fields = c("alias", "concept", "title"),
            apropos, keyword, whatis, ignore.case = TRUE,
            package = NULL, lib.loc = NULL,
            help.db = getOption("help.db"),
            verbose = getOption("verbose"),
            rebuild = FALSE, agrep = NULL)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{pattern}] a character string to be matched in the specified
fields.  If this is given, the arguments \code{apropos},
\code{keyword}, and \code{whatis} are ignored.
\item[\code{fields}] a character vector specifying the fields of the help
data bases to be searched.  The entries must be abbreviations of
\code{"name"}, \code{"title"}, \code{"alias"}, \code{"concept"}, and
\code{"keyword"}, corresponding to the help page's (file) name, its
title, the topics and concepts it provides documentation for, and
the keywords it can be classified to.
\item[\code{apropos}] a character string to be matched in the help page
topics and title.
\item[\code{keyword}] a character string to be matched in the help page
keywords.
\item[\code{whatis}] a character string to be matched in the help page
topics.
\item[\code{ignore.case}] a logical.  If \code{TRUE}, case is ignored during
matching; if \code{FALSE}, pattern matching is case sensitive.
\item[\code{package}] a character vector with the names of packages to
search through, or \code{NULL} in which case \emph{all} available
packages in the library trees specified by \code{lib.loc} are
searched.
\item[\code{lib.loc}] a character vector describing the location of \R{}
library trees to search through, or \code{NULL}.  The default value
of \code{NULL} corresponds to all libraries currently known.
\item[\code{help.db}] a character string giving the file path to a previously
built and saved help data base, or \code{NULL}.
\item[\code{verbose}] logical; if \code{TRUE}, the search process is traced.
\item[\code{rebuild}] a logical indicating whether the help data base should
be rebuilt.
\item[\code{agrep}] if \code{NULL} (the default) and the character string to
be matched consists of alphanumeric characters, whitespace or a dash
only, approximate (fuzzy) matching via \code{\Link{agrep}} is used
unless the string has fewer than 5 characters; otherwise, it is
taken to contain a regular expression to be matched via
\code{\Link{grep}}.  If \code{FALSE}, approximate matching is not
used.  Otherwise, one can give a numeric or a list specifying the
maximal distance for the approximate match, see argument
\code{max.distance} in the documentation for \code{\Link{agrep}}.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
Upon installation of a package, a contents data base which contains
the information on name, title, aliases and keywords and, concepts
starting with \R{} 1.8, is computed from the Rd files in the package and
serialized as \file{Rd.rds} in the \file{Meta} subdirectory of the
top-level package installation directory (or, prior to \R{} 1.7, as
\file{CONTENTS} in Debian Control Format with aliases and keywords
collapsed to character strings in the top-level package installation
directory).  This, or a pre-built help.search index serialized as
\file{hsearch.rds} in the \file{Meta} directory, is the data base
searched by \code{help.search()}.

The arguments \code{apropos} and \code{whatis} play a role similar to
the Unix commands with the same names.

If possible, the help data base is saved to the file \file{help.db} in
the \file{.R} subdirectory of the user's home directory or the current
working directory.

Note that currently, the aliases in the matching help files are not
displayed.\end{Details}
\begin{Value}
The results are returned in an object of class \code{"hsearch"}, which
has a print method for nicely displaying the results of the query.
This mechanism is experimental, and may change in future versions of
R.\end{Value}
\begin{SeeAlso}\relax
\code{\Link{help}};
\code{\Link{help.start}} for starting the hypertext (currently HTML)
version of \R's online documentation, which offers a similar search
mechanism.

\code{\Link{apropos}} uses regexps and has nice examples.\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
help.search("linear models")    # In case you forgot how to fit linear
                                # models
help.search("non-existent topic")
## Don't run: 
help.search("print")            # All help pages with topics or title
                                # matching 'print'
help.search(apropos = "print")  # The same

help.search(keyword = "hplot")  # All help pages documenting high-level
                                # plots.

## Help pages with documented topics starting with 'try'.
help.search("\\btry", fields = "alias")
## Do not use '^' or '$' when matching aliases or keywords
## (unless all packages were installed using R 1.7 or newer).
## End Don't run
\end{ExampleCode}
\end{Examples}

